1. Field of Invention
The present invention relates to the manufacture of silicon wafers and, more specifically, to a method of using a filter to control non-uniformities in wafer processing using resonant heating.
2. Description of Prior Art
Silicon wafers may be processed using plasma etch reactors. Layers of conducting or insulating material are deposited onto a silicon wafer and circuit features are etched into the wafer by bombarding the wafer with a reactive gas and an ion stream in near-vacuum conditions to carve out circuit features. Plasma processing has some drawbacks, however, as it often results in spatial non-uniformity at both the wafer and chip scale.
At the wafer scale, the design of the plasma chamber can adversely affect the gas flow profiles and the plasma itself may exacerbate etching at the wafer edge due to the high density of hot electrons and radicals. At the chip scale, loading adversely affects etch profiles that, for example, may have isolated to nested bias. As a result of these shortcomings, the full capability of plasma etching is unrealized and the overall process yields lower amounts of finished product than otherwise possible.
Some attempts to alleviate center/edge non-uniformity involve cooling the backside of the wafer with helium. This method does not provide selective or precise control over the etching process, however, as the temperature gradients are smoothed from the back to the front of the wafer and the same chilling substance is used for all zones. Additionally, the plasma heating generally dominates the thermal characteristics of the wafer surface, thereby reducing the impact of any helium cooling.
Other attempts to overcome the disadvantages of plasma processing involve the use of masks that reduce the amount of IR heating to selected areas of the wafer or multiple energy sources for differential heating. The systems are generally limited to inhibiting heating at the edge of the wafer or are extremely limited in their ability to provide high-resolution selection.